Satellite television receiving systems usually comprise an “outdoor unit” including a dish-like receiving antenna and a “block” converter, and an “indoor unit” including a tuner and a signal processing section. The block converter converts the entire range (“block”) of relatively high frequency RF signals transmitted by a satellite to a more manageable, lower range of frequencies.
In a conventional satellite television transmission system, television information is transmitted in analog form and the RF signals transmitted by the satellite are in the C (e.g., 3.7 to 4.2 GHz) and Ku (e.g., 11.7 to 14.2 GHz) bands. The RF signal received from the satellite by the antenna of the receiving system are converted by the block converter to the L band (e.g., 900 to 2000 MHz). An RF filter section of the tuner of the indoor unit selects the one of the RF signals received from the block converter corresponding to the selected channel, and a mixer/local oscillator section of the tuner converts the selected RF signal to a lower, intermediate frequency (IF) range for filtering and demodulation.
In newer satellite television systems, such as the DirecTv™ operated by the Hughes Corporation of California, television information is transmitted in digital form. The RF signals are transmitted by the satellite in the Ku band, and are converted by the block converter to the L band. The frequency range of the RF signals transmitted by the satellite is somewhat smaller (e.g., between 12.2 and 12.7 GHz) than that for the analog satellite television system, and the frequency range of RF signals produced by the block converter is accordingly somewhat smaller (e.g., between 950 and 1450 MHz).
In a digital satellite television broadcast system, the television information is digitized, compressed and organized into a series or stream of data packets corresponding to respective video, audio, and data portions of the television information. The digital data is modulated on to a RF carrier signal in what is known as QPSK (Quaternary Phase Shift Keying) modulation and the RF signal is transmitted to a satellite in earth orbit, from which it is retransmitted back to the earth.
In QPSK modulation, the phases of two quadrature phase signals, I and Q, are controlled in response to the bits of respective digital data streams. For example, the phase is set to 0 degrees (.degree.) in response to a low logic level (“0”), and the phase is set to 180.degree. in response to a high logic level (“1”). The phase shift modulated I and Q signals are combined and the result transmitted as a QPSK modulated RF carrier signal. Accordingly, each symbol of the modulated QPSK carrier indicates one of four logic states, i.e., 00, 01, 10 and 11
The conversion stage of the block converter of the outdoor unit is powered by a DC voltage supplied by the indoor unit. The satellite television signal receivers are typically located at the subscriber's residence. When a problem with the system occurs, it is desirable for the service provider to be able to remotely diagnose the problems with the receiver, thereby possibly avoiding having to send a service technician to the remote location. If the problem is simple enough, instructions can be given to the subscriber, and the problem immediately remedied. If the problem is too complex for the subscriber to remedy, or there is an equipment failure, advanced information on the problem can be provided to the service technician, thereby allowing the technician to bring the required parts or equipment to the subscriber's location. Among the parameters desirable to be diagnosed remotely is the low noise block (LNB) line voltage. In addition to supplying operating power to the LNB, different LNB line voltages are used to select between different signals or polarizations of signals received by the LNB. There are defined ranges for each of the two allowed voltages. In order to diagnose certain kinds of problems in the receiving system, it is desirable to know with reasonable accuracy what voltage is being presented on the antenna connector at the back of the indoor unit. Having greater knowledge of the voltage allows better decision-making in determining cause and effect of problems in the receiving system. Knowing that the LNB line voltage is somewhere between or very, very close to one limit of allowable voltage is more desirable than just an indication of the voltage is higher than the allowable band for the lower voltage setting.